1. Field of the Invention
The present invention relates to mobile video telephony and, in particular, to a call control system and method for mobile video telephony that enable an automatic call setup between a mobile video telephony terminal and a mobile audio-dedicated terminal.
2. Description of the Related Art
Video telephony is a service that enables participants to communicate while viewing each other in real time. Video telephony can be implemented with a switch-based circuit switching network or a packet switched All-IP network.
In order to implement video telephony over a mobile IP, H.323 and H.324M standards developed by the International Telecommunications Union (ITU) are recommended.
H.323 is a protocol designed to provide teleconferencing with voice, video, and data capabilities on packet switching networks, and H.324 is a protocol for sharing voice, video and data over an analog telephone line. Meanwhile, H.324M refers to a “mobile” extension of H.324 protocol developed by the ITU.
H.324M uses H.261 and H.263 as video codecs and G.723.1 as an audio codec. H.261 is a digital video coding standard designed for compressing and coding video data, and H263 and MPEG-4 are enhanced video codecs for compressed encoding for video conferencing. G.723.1 is an audio codec providing 8 Kbps codec bit rate.
The Third Generation Partnership Project has adopted H.324M as a standard for conversational video-telephony over 3G, which is named 3G-324M. 3G-324M differs from H.324M in that it uses an Adaptive Multi-Rate (AMR) codec as the basic voice codec, and G.723.1 is optional.
In addition, H.324 uses H.223 protocol for multiplexing voice, video, and data; and H.245 protocol as a control protocol for selecting a voice codec and assigning channels for a point-to-point or a point-to-multipoint connection.
In the case of a video communication service using H.324M, two terminals establish a call connection through a call establishment procedure. Between the two terminals, an audiovisual link is established.
However, the conventional audiovisual communication service has a limitation in establishing a communication link between a video communication-enabled terminal and an audio-dedicated terminal. If a called party terminal does not support the audiovisual communication function, a communication channel cannot be established. In this case, the calling party terminal receives a message informing the calling party that the called party terminal cannot respond to the audiovisual communication call. That is, the calling party terminal does not know the capacity of the called party terminal before the call is initiated, and hence it periodically attempts audiovisual communication with the called party terminal without recognizing that the called party terminal is an audio-dedicated terminal that does not support the audiovisual communication service.